Indicators that facilitate intraoral scanning

ABSTRACT

A processing device of a system makes a comparison between a current image of an oral cavity of a patient and one or more previously received images of the oral cavity of the patient, the current image and the one or more previously received images having been generated by an intraoral scanner. The processing device determines an amount of overlap between a current field of view of the intraoral scanner and topography scans of the oral cavity based on the comparison. The processing device outputs a warning indicator associated with a positioning of the current field of view of the intraoral scanner responsive to determining that the amount of overlap fails to meet or exceed an overlap threshold.

CROSS-REFERENCE

This application is a continuation application of U.S. application Ser.No. 17/592,424, filed Feb. 3, 2022, which is a continuation applicationof U.S. application Ser. No. 17/133,344, filed Dec. 23, 2020, which is acontinuation application of U.S. application Ser. No. 16/842,645, filedApr. 7, 2020, now U.S. Pat. No. 10,888,401, issued Jan. 12, 2021, whichis a continuation application of U.S. application Ser. No. 16/599,589,filed Oct. 11, 2019, now U.S. Pat. No. 10,660,732, issued May 26, 2020,which is a continuation of U.S. application Ser. No. 15/974,072, filedMay 8, 2018, now U.S. Pat. No. 10,485,639, issued Nov. 26, 2019, whichis a continuation application of U.S. application Ser. No. 15/645,243,filed Jul. 10, 2017, now U.S. Pat. No. 9,987,108, issued Jun. 5, 2018,which is a continuation application of U.S. application Ser. No.14/463,464, filed Aug. 19, 2014, now U.S. Pat. No. 9,724,177, issuedAug. 8, 2017, which are incorporated herein by reference in theirentirety and to which applications we claim priority under 35 USC § 120.

BACKGROUND OF THE INVENTION

Many dental and orthodontic procedures require accuratethree-dimensional (3D) topographical measurements of a patient'sintraoral cavity. For example, in the design and fabrication of dentalprostheses (e.g., crowns or bridges), 3D models of the prosthesis siteand surrounding dentition are typically used to ensure proper fit of theprosthesis. In many orthodontic procedures, 3D models of the patient'sdental arches are utilized to design orthodontic appliances and developtreatment plans (e.g., to correct malocclusions). Various approaches canbe used to produce such 3D models. For example, a physical model can beconstructed from an impression of the patient's dentition.Alternatively, the intraoral cavity can be scanned to provide a virtualmodel suitable for use within computer-assisted design andcomputer-assisted manufacture (CAD/CAM) methods as well as digitaltreatment planning.

Scanning of the intraoral cavity may be performed by a dental ororthodontic practitioner. Previous methods and systems for scanning theintraoral cavity, however, can be less than ideal with regards toproviding guidance to the dental or orthodontic practitioner during thescanning procedure. As a result, incomplete scanning coverage orinsufficient overlap between scans may reduce the accuracy of thesubsequent digital model. Conversely, excessive overlap between scanscan be inefficient and unnecessarily lengthen the duration of thescanning procedure.

Thus, there is a need for improved methods and systems for scanning anintraoral cavity of a patient.

SUMMARY

Embodiments provide improved methods and systems for scanning anintraoral cavity of a patient. In many embodiments, methods and systemsfor scanning an intraoral cavity comprise displaying a viewfinder imagecorresponding to a field of view of an intraoral scanner and one or moreindicators depicting previously scanned portions of the intraoralcavity. The scanning methods and systems described herein can providereal-time visual guidance of scanning coverage of the intraoral cavity,thereby providing faster and more efficient intraoral scanning. In manyembodiments, an optical axis of the scanner is aligned with an opticalaxis of the viewfinder in order to determine the scanned portions of theintraoral cavity directly from the viewfinder images. Determining thescanned portions of the intraoral cavity from the viewfinder images canprovide faster scanning and improve real-time display of the scannedportions of the intraoral cavity with the real-time images shown to theuser, which can facilitate alignment of the scanner with the intraoralcavity.

In a first aspect, a method for scanning an intraoral cavity of apatient comprises capturing one or more viewfinder images of one or moreportions of the intraoral cavity of the patient, each of said one ormore viewfinder images corresponding to a field of view of an intraoralscanner, and scanning the one or more portions of the intraoral cavitywith the intraoral scanner to generate one or more topography scans ofthe one or more portions of the intraoral cavity. The one or moretopography scans may correspond to the one or more viewfinder images.The method may further comprise capturing a viewfinder image of aportion of the intraoral cavity, the viewfinder image overlapping withthe one or more viewfinder images. An area of overlap of the viewfinderimage with the one or more viewfinder images can be determined. One ormore indicators of the area of overlap can be displayed on one or morelocations of a display in order to provide guidance for positioning thefield of view of the intraoral scanner.

In another aspect, a system for scanning an intraoral cavity of apatient comprises an intraoral scanner, a viewfinder, a display, and aprocessing unit. The intraoral scanner can comprise an optical assemblyconfigured to focus light onto one or more portions of the intraoralcavity in order to generate one or more topography scans of the one ormore portions. The viewfinder can be optically aligned with theintraoral scanner in order to capture one or more viewfinder imagescorresponding to the field of view of the intraoral scanner. The displaycan be configured to display one or more indicators on one or morelocations in order to provide guidance for positioning the field of viewof the intraoral scanner. The processing unit can be operatively coupledto the intraoral scanner, the display, and the viewfinder. Theprocessing unit can comprise instructions to determine an area ofoverlap between the viewfinder image captured by the viewfinder and oneor more viewfinder images captured by the viewfinder. The one or moreviewfinder images can correspond to the one or more topography scansgenerated by the intraoral scanner. The processing unit can compriseinstructions to show the area of overlap of the viewfinder image and theone or more viewfinder images on the display.

Other benefits and features of embodiments the present invention will beapparent in view of the specification, claims, and appended figures.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIGS. 1A and 1B schematically illustrate, by way of a block diagram, anapparatus in accordance with many embodiments (FIG. 1B is a continuationof FIG. 1A);

FIG. 2A illustrates a top view of a probing member in accordance withmany embodiments;

FIG. 2B illustrates a longitudinal cross-section through the probingmember of FIG. 2A, depicting exemplary rays passing therethrough;

FIG. 3 illustrates a system for scanning an intraoral cavity, inaccordance with many embodiments;

FIG. 4 illustrates an optical system with aligned scanner and viewfinderoptics, in accordance with many embodiments;

FIG. 5A illustrates a method for guiding scanning of an intraoral cavityof a patient, in accordance with many embodiments;

FIG. 5B illustrates a method for determining overlap between a currentviewfinder image and previous scanning cover, in accordance with manyembodiments;

FIG. 5C illustrates a method for tracking scanning progress, inaccordance with many embodiments;

FIGS. 6A, 6B, and 6C illustrate viewfinder images with overlaidindicators, in accordance with many embodiments; and

FIG. 7 illustrates a user interface suitable for use with an intraoralscanning system, in accordance with many embodiments.

DETAILED DESCRIPTION

Methods and systems described herein provide visual guidance for a user(e.g., a dental or orthodontic practitioner) during an intraoralscanning procedure. The method and systems described herein can becombined in many ways and are well suited for combination for intraoralscanners used for measuring portions of the intraoral cavity, forexample. Any of the embodiments provided herein can be combined withother embodiments to the extent that such embodiments are notinconsistent with the teachings described herein.

As used herein A and/or B encompasses A alone, B alone, and combinationsof A and B.

In many embodiments, one or more indicators depicting previously scannedportions of the intraoral cavity are displayed as an overlay on aviewfinder image depicting the field of view of an intraoral scanner.The one or more indicators can be updated as the scanner is moved, suchthat the user receives real-time visual guidance of scanning coverageand progress during the scanning procedure. Based on the displayedindicators, the practitioner can adjust the position of the scannerwithin the intraoral cavity to control the amount of overlap between thescans and ensure satisfactory scanning coverage of the region ofinterest. The embodiments provided herein can be used to improve theefficiency and ease of use of intraoral scanning systems.

In one aspect, a method is provided for scanning an intraoral cavity ofa patient. In many embodiments, the method comprises capturing one ormore viewfinder images of one or more portions of the intraoral cavityof the patient, each of said one or more viewfinder images correspondingto a field of view of an intraoral scanner, and scanning the one or moreportions of the intraoral cavity with an intraoral scanner to generateone or more topography scans of the one or more portions of theintraoral cavity. The one or more topography scans may correspond to theone or more viewfinder images. The method further comprises capturing aviewfinder image of a portion of the intraoral cavity, the viewfinderimage overlapping with the one or more viewfinder images. An area ofoverlap of the viewfinder image with the one or more viewfinder imagescan be determined. One or more indicators of the area of overlap can bedisplayed on one or more locations of a display in order to provideguidance for positioning the field of view of the intraoral scanner.

In many embodiments, the display and one or more indicators providevisual guidance representing the area of overlap on a viewfinder image.For example, the one or more indicators may mark one or more boundarylocations of the area of overlap or may identify a boundary of the areaof overlap. The one or more indicators on the one or more locations ofthe display may move on the display when a user adjusts the portion ofthe intraoral cavity within the field of view of the intraoral scannerin order to allow the user to position the field of view of theintraoral scanner. The method may further comprise scanning the portionof the intraoral cavity with the one or more indicators displayed at theone or more locations on the display. Subsequent viewfinder images canbe shown with the one or more indicators shown at the one or morelocations on the display. Optionally, the one or more viewfinder imagescan comprise a warning indicator if the area of overlap is smaller thana predetermined amount.

The area of overlap can be determined using any suitable technique. Inmany embodiments, the one or more viewfinder images are compared to theviewfinder image in order to determine the area of overlap of theviewfinder image with the one or more viewfinder images corresponding tothe one or more topography scans. Determining the area of overlap maycomprise registering the viewfinder image to the one or more viewfinderimages. For example, registering the viewfinder image to the one or moreviewfinder images can comprise identifying one or more features presentin both the viewfinder image and the one or more viewfinder images.Registering the viewfinder image to the one or more viewfinder imagescan comprise at least one of transforming or deforming the viewfinderimage to increase it similarity to the one or more viewfinder images.

Following the determination and display of the one or more indicators,intraoral topography scans can be generated using the indicators as avisual guide for aiming the scanner. In many embodiments, the methodfurther comprises positioning the intraoral scanner within the intraoralcavity guided at least in part by the one or more indicators. A portionof the intraoral scanner can be scanned to obtain a topography scanthereof. The method may further comprise recording a viewfinder imagecorresponding to the topography scan while scanning the portion of theintraoral cavity with the intraoral scanner. The one or more viewfinderimages can be updated to include the recorded viewfinder image.

In another aspect, a system is provided for scanning an intraoral cavityof a patient. In many embodiments, the system comprises an intraoralscanner, a viewfinder, a display, and a processing unit. The intraoralscanner can comprise an optical assembly configured to focus light ontoone or more portions of the intraoral cavity in order to generate one ormore topography scans of the one or more portions. The viewfinder can beoptically aligned with the intraoral scanner in order to capture one ormore viewfinder images corresponding to the field of view of theintraoral scanner. The display can be configured to display one or moreindicators on one or more locations in order to provide guidance forpositioning the field of view of the intraoral scanner. The processingunit can be operatively coupled to the intraoral scanner, the display,and the viewfinder. The processing unit can comprise instructions todetermine an area of overlap between the viewfinder image captured bythe viewfinder and one or more viewfinder images captured by theviewfinder. The one or more viewfinder images can correspond to the oneor more topography scans generated by the intraoral scanner. Theprocessing unit can comprise instructions to show the area of overlap ofthe viewfinder image and the one or more viewfinder images on thedisplay.

The design of the intraoral scanner can be varied as desired. In manyembodiments, the intraoral scanner configured for point-and-shootscanning. Alternatively, the intraoral scanner can be configured forcontinuous scanning.

Various approaches can be used to determine the area of overlap. In manyembodiments, the processing unit comprises instructions to determine thearea of overlap by registering the viewfinder image to the one or moreviewfinder images. Registering the viewfinder image to the one or moreviewfinder images can comprise identifying one or more features presentin the viewfinder image and the one or more viewfinder images.Registering the viewfinder image to the one or more viewfinder imagescan comprise at least one of transforming or deforming the viewfinderimage to increase its similarity to the one or more viewfinder images.

The indicators can include any graphical element suitable forrepresenting the area of overlap. In many embodiments, the one or moreindicators comprise a boundary of the area of overlap or a coloring ofthe area of overlap. The one or more indicators can comprise a warningindicator if the area of overlap is smaller than a predetermined amount.

In many embodiments, the processing unit comprises instructions torecord the viewfinder image while the intraoral scanner is scanning theintraoral cavity and add the recorded viewfinder image to the one ormore viewfinder images.

In many embodiments, the display unit is configured to display surfacetopography data of the one or more portions of the intraoral cavity.

Turning now to the drawings, in which like numbers and/or wordsdesignate like elements in the various figures, FIGS. 1A and 1Billustrate an apparatus 20 for measuring surface topography optically.The apparatus 20 includes an optical device 22 coupled to a processor24. The embodiment illustrated in FIGS. 1A and 1B is particularly usefulfor measuring surface topography of a patient's teeth 26. For example,the apparatus 20 can be used to measure surface topography of a portionof the patient's teeth where at least one tooth or portion of tooth ismissing to generate surface topography data for subsequent use in designand/or manufacture of a prosthesis for the patient (e.g., a crown or abridge). It should be noted, however, that the invention is not limitedto measuring surface topography of teeth, and applies, mutatis mutandis,also to a variety of other applications of imaging of three-dimensionalstructure of objects (e.g., for the recordal of archeological objects,for imaging of a three-dimensional structure of any suitable item suchas a biological tissue, etc.).

The optical device 22 includes, in the illustrated embodiment, a lightsource 28 such as a semiconductor laser unit emitting a laser light, asrepresented by arrow 30. The light passes through a polarizer 32, whichcauses the light passing through the polarizer 32 to have a certainpolarization. The light then enters into an optic expander 34, whichincreases the diameter of the light beam 30. The light beam 30 thenpasses through a module 38, which can, for example, be a grating or amicro lens array that splits the parent beam 30 into a plurality oflight beams 36, represented here, for ease of illustration, by a singleline.

The optical device 22 further includes a partially transparent mirror 40having a small central aperture. The mirror 40 allows transfer of lightfrom the laser unit 28 through the downstream optics, but reflects lighttravelling in the opposite direction. It should be noted that inprinciple, rather than a partially transparent mirror, other opticalcomponents with a similar function may be used (e.g., a beam splitter).The aperture in the mirror 40 improves the measurement accuracy of theapparatus. As a result of this mirror structure, the light beams producea light annulus on the illuminated area of the imaged object as long asthe area is not in focus. The annulus becomes a sharply-focusedilluminated spot when the light beam is in focus relative to the imagedobject. Accordingly, a difference between the measured intensity whenout-of-focus and in-focus is larger. Another advantage of a mirror ofthis kind, as opposed to a beam splitter, is that internal reflectionsthat occur in a beam splitter are avoided, and hence the signal-to-noiseratio is greater.

The optical device 22 further includes confocal optics 42, typicallyoperating in a telecentric mode, relay optics 44, and an endoscopicprobe member 46. In many embodiments, the confocal optics 42 isconfigured to avoid distance-introduced magnification changes andmaintain the same magnification of the image over a wide range ofdistances in the Z direction (the Z direction being the direction ofbeam propagation). In many embodiments, the relay optics 44 isconfigured to maintain a certain numerical aperture of the light beam'spropagation.

The endoscopic probe member 46 can include a light-transmitting medium,which can be a hollow object defining within it a light transmissionpath or an object made of a light transmitting material (e.g., a glassbody or tube). The light-transmitting medium may be rigid or flexible(e.g., fiber optics). In many embodiments, the endoscopic probe member46 includes a mirror 95 of the kind ensuring a total internal reflectionand directing the incident light beams towards the patient's teeth 26.The endoscope 46 thus emits a plurality of incident light beams 48impinging on to the surface of the patient's teeth 26.

In many embodiments, the distance between the endoscopic probe member 46and the patient's teeth 26 is determined by measuring one or morecharacteristics of returning light beams 54 generated by illuminatingthe teeth 26 with the incident light beams 48. Such characteristics caninclude, for example, intensity, wavelength, polarization, phase shift,interference, and/or dispersion of the returning light beams 54. Anydescription herein relating to light intensity can also be applied toother suitable characteristics of light, and vice-versa. Themeasurements of the characteristic(s) can be used to detect whether theincident light beams 46 are focused on the surface of the teeth 26 andthereby determine the distance between the endoscopic probe member 46and the teeth 26.

For example, as depicted in FIGS. 1A and 1B, the distance can bedetermined based on measured light intensities. The incident light beams48 form an array of light beams arranged in an X-Y plane, relative to aCartesian reference frame 50, and propagating along the Z axis. When theincident light beams 48 are incident upon an uneven surface, resultingilluminated spots 52 are displaced from one another along the Z axis, atdifferent (X_(i), Y_(i)) locations. Thus, while an illuminated spot 52at one location may be in focus for a given focal length produced by theconfocal optics 42, illuminated spots 52 at other locations may beout-of-focus. Therefore, the light intensity of the returned light beamsof the focused spots will be at its peak, while the light intensity atother spots will be off peak. Thus, for each illuminated spot, aplurality of measurements of light intensity are made at differentpositions along the Z-axis and for each of such (X_(i), Y_(i))locations, typically the derivative of the intensity over distance (Z)will be made, and the Z_(i) yielding maximum derivative, Z₀, will be thein-focus distance. As pointed out above, where, as a result of use ofthe mirror with aperture 40, the incident light forms a light disk onthe surface when out of focus and a sharply-focused light spot only whenin focus, the distance derivative will be larger when approachingin-focus position thus increasing accuracy of the measurement.

The light reflected from each of the illuminated spots 52 includes abeam travelling initially in the Z axis in the opposite direction of theoptical path traveled by the incident light beams. Each returned lightbeam 54 corresponds to one of the incident light beams 36. Given theunsymmetrical properties of mirror 40, the returned light beams 54 arereflected in the direction of a detection assembly 60. The detectionassembly 60 includes a polarizer 62 that has a plane of preferredpolarization oriented normal to the polarization plane of polarizer 32.The returned polarized light beam 54 pass through an imaging optics 64,typically a lens or a plurality of lenses, and then optionally throughan array of pinholes 66. Each returned light beam 54 may pass at leastpartially through a respective pinhole of the array of pinholes 66. Acharge-coupled device (CCD) sensor array 68 includes a matrix of sensingelements. In many embodiments, each sensing element represents a pixelof the image and each sensing element corresponds to one pinhole in thearray 66.

The sensor array 68 is connected to an image-capturing module 80 of theprocessor unit 24. The light intensity measured by each of the sensingelements of the sensor array 68 is analyzed, in a manner describedbelow, by the processor 24.

The optical device 22 includes a control module 70 that controlsoperation of the light source 28. The control module 70 can be used inconjunction with any suitable mechanism or configuration for controllingthe focal positions of the incident light beams 36. For example, in manyembodiments, a motor 72 is drivingly coupled with the confocal optics 42so as to scan the focus of the light beams through a range of focaldepths along the Z axis. In a single sequence of operation, the controlunit 70 induces motor 72 to reconfigure the confocal optics 42 to changethe focal plane location and then, after receipt of a feedback that thelocation has changed, the control module 70 induces the laser 28 togenerate a light pulse. The control module 70 synchronizes the operationof the image-capturing module 80 with the operation of the confocaloptics 42 and the light source 28 during acquisition of datarepresentative of the light intensity from each of the sensing elements.Then, in subsequent sequences, the confocal optics 42 causes the focalplane to change in the same manner and intensity data acquisitioncontinues over a range of focal lengths.

The intensity data is processed by the processor 24 per processingsoftware 82 to determine relative intensity in each pixel over theentire range of focal planes of confocal optics 42. As explained above,once a certain light spot is in focus on the three-dimensional structurebeing measured, the measured intensity of the returning light beam willbe maximal. Thus, by determining the Z_(i) corresponding to the maximallight intensity or by determining the minimum derivative of the lightintensity, for each pixel, the relative in-focus focal length along theZ axis can be determined for each light beam. Thus, data representativeof the three-dimensional topography of the external surfaces of theteeth is obtained. A resulting three-dimensional representation can bedisplayed on a display 84 and manipulated for viewing (e.g., viewingfrom different angles, zooming-in or out) by a user control module 85(e.g., a computer keyboard). In addition, the data representative of thesurface topology can be transmitted through an appropriate data portsuch as, for example, a modem 88 or any suitable communication network(e.g., a telephone network) to a recipient (e.g., to an off-site CAD/CAMapparatus).

By capturing, in this manner, relative distance data between the probeand the structure being measured from two or more angular locationsaround the structure (e.g., in the case of a teeth segment, from thebuccal direction, lingual direction and/or optionally from above theteeth), an accurate three-dimensional representation of the structurecan be generated. The three-dimensional data and/or the resultingthree-dimensional representation can be used to create a virtual modelof the three-dimensional structure in a computerized environment and/ora physical model fabricated in any suitable fashion (e.g., via acomputer controlled milling machine, a rapid prototyping apparatus suchas a stereolithography apparatus).

As already pointed out above, a particular and preferred application isimaging of a segment of teeth having at least one missing tooth or aportion of a tooth. The resulting three-dimensional surface topographydata can, for example, be used for the design and subsequent manufactureof a crown or any other prosthesis to be fitted into this segment.

Referring now to FIGS. 2A and 2B, a probing member 90 is illustrated inaccordance with many embodiments. The probing member 90 can be made of alight transmissive material (e.g., glass, crystal, plastic, etc.) andincludes a distal segment 91 and a proximal segment 92, tightly gluedtogether in an optically transmissive manner at 93. A slanted face 94 iscovered by a reflective mirror layer 95. A transparent disk 96 (e.g.,made of glass, crystal, plastic, or any other transparent defining asensing surface 97 is disposed along the optical path distal to themirror layer 95 so as to leave an air gap 98 between the glass disk 96and the distal segment 91. The transparent disk 96 is fixed in positionby a holding structure (not shown). Three light rays 99 are representedschematically. As can be seen, the light rays 99 reflect from the wallsof the probing member 90 at an angle in which the walls are totallyreflective, reflect from the mirror layer 95, and then propagate throughthe sensing face 97. The light rays 99 are focused on a focusing plane100, the position of which can be changed by the confocal optics 42.

FIG. 3 illustrates the main elements of a system 200 for scanning anintraoral cavity, in accordance with many embodiments. The system 200includes an input unit 210 (e.g., a keyboard, mouse, joystick, tablet,or touch screen), a display or output module 220 (e.g. a screen,monitor, or printer), a processing unit 230 (e.g., comprising one ormore processors such as a CPU), and a memory 240. A handheld scanner 250(e.g., an intraoral scanner) is operatively connected to the system 200.Any suitable scanning system or device for obtaining 3D topographicaldata of the intraoral cavity can be used for the scanner 250, such asthe optical device 22. For example, the scanner 250 can be a“point-and-shoot” scanner configured such that each scan event isinitiated by a specific user input command (e.g., a button press, mouseclick, etc). In such embodiments, each scan can be performed while thescanner 250 is held stationary at a desired position and orientation. Asanother example, the scanner 250 can be a “continuous scanner”configured to continuously obtain scan data without requiring user inputto specifically initiate each scan (e.g., based on control signalsproduced by the processing unit 230). In such embodiments, scanning canbe performed continuously or at predetermined time intervals as thescanner 250 moves through a plurality of positions and orientationsrelative to the intraoral cavity. Scan data collected by the scanner 250can be processed by the processing unit 230 to reconstruct the surfacetopography of the intraoral cavity, thereby generating a 3D digitalmodel of the intraoral cavity. The surface topography data can bepresented to the user (e.g., as a 3D graphical representation on thedisplay 220) and/or stored for subsequent applications (e.g., in thememory 240).

In many embodiments, the intraoral scanning systems provided hereininclude a viewfinder that provides two-dimensional image data of theintraoral cavity corresponding to the field of view of the scanner. Inmany embodiments, the viewfinder and scanner are optically aligned suchthat the field of view of the viewfinder is the same or similar to thefield of view of the scanner. The viewfinder images can be displayed toa user in order to guide the scanning procedure and can be updated asthe scanner moves to reflect changes in the scanner's field of view.Accordingly, the user can adjust the position and orientation of thescanner based on the displayed viewfinder images in order to ensuresatisfactory scanning coverage of the targeted portion of the intraoralcavity.

The approaches provided herein can be used with any suitable scanner andviewfinder system. The viewfinder can include any suitable imagingdevice operable to provide images corresponding to the field of view ofthe scanner, such as a camera suitable for capturing monochromatic orcolor image data. For example, the viewfinder images may represent thefield of view of the scanner, e.g., in terms of viewing angle, coveragearea, etc. The viewfinder field of view may be similar to or larger thanthe scanner field of view, such that the viewfinder images represent theentirety of the field of view of the scanner. Alternatively, theviewfinder field of view may be smaller than or partially overlappingwith the scanner field of view, such that the viewfinder imagesrepresent a subset of the field of view of the scanner. In manyembodiments, the viewfinder is adapted to record image data in realtime, such that the viewfinder images are continuously displayed andupdated as the scanner is moved. For example, the viewfinder can includea camera with a suitable video capture rate for real-time display.Alternatively, the viewfinder can record image data at a video capturerate different than the video display rate.

FIG. 4 illustrates an optical system 300 with aligned scanner andviewfinder optics, in accordance with many embodiments. At least some ofthe elements of the optical system 300 can be combined with the othersystems and devices described herein. For example, the optical system300 can be incorporated within the apparatus 20, which may be part ofthe scanning system 200. In many embodiments, at least some of thecomponents of the optical system 300 form part of an intraoral scanningdevice, such as the handheld scanner 250. In the system 300, thecomponents of the scanner and viewfinder are integrated into a singledevice, such at least some portions of the optical path of the scanneroverlap with the optical path of the viewfinder and at least someoptical components of the system 300 are shared between the scanner andviewfinder. The system 300 comprises a scanner illumination unit 302that produces a two-dimensional array of light beams 304 (e.g., an arrayof laser beams) for surface topography scanning. The array of lightbeams 304 can propagate through a polarizing beam splitter 306, a firstset of lens elements 308, a second set of lens elements 310, and aprobing member 90 so as to illuminate the surface of a targeted objectwith a two-dimensional array of light spots. In many embodiments, thearray of light beams 304 is focused to a focal plane 314 external to theprobing member 90. Light beams reflected from the surface can pass backthrough the probing member 90 and lens elements 308, 310 and aredirected by the beam splitter 306 onto an detector unit 316 (e.g.,sensor array 68). The detector unit 316 can include a plurality ofsensor elements used to measure characteristics of the returning light(e.g., light intensity) in order to determine the surface topography, aspreviously described herein.

The system 300 also includes a viewfinder illumination unit 318 thatprovides a plurality of light beams 320 for generating viewfinder imagedata. For example, the viewfinder illumination unit 318 can include aplurality of LEDs. The LEDs can be arranged in a ring configuration,with the central aperture of the ring sized to permit light beams of thearray 304 and returning light beams from the object surface to passthrough. The light beams 320 produced by the viewfinder illuminationunit 318 can propagate through the second set of lens elements 310 andthe probing member 90 to illuminate the object surface. Light reflectedfrom the surface can pass back through the optics and onto the sensorelements of the detector unit 316, as described above. The sensor datacan subsequently be processed using techniques known to those of skillin the art to provide viewfinder images. In many embodiments, thescanner and viewfinder optics are optically aligned so as to share acommon optical axis 322, such that the field of view of the scanner isthe same or similar to the field of view of the viewfinder and theviewfinder images provided by the viewfinder correspond to the field ofview of the scanner.

In many embodiments, the system 300 can utilize a single detector unit316 to generate scan data and viewfinder image data, rather than havingseparate detector units for topography scanning and image capture.Alternatively, the system 300 may comprise separate detectors forgenerating scanning data from the array of light beams 304 and forgenerating viewfinder image data, in which the scanner and viewfinderoptical axes are optically aligned, for example.

The viewfinder illumination unit 318 can be adapted to providemonochromatic or polychromatic illumination (e.g., via colored LEDs). Inmany embodiments, the illumination unit 318 sequentially illuminates thetargeted object with different wavelengths (e.g., red, green, and bluewavelengths) and the detector unit 316 obtains a monochromatic imagecorresponding to each wavelength. The different monochromatic images canbe subsequently be processed and merged to provide a composite colorimage of the object. Optionally, the system 300 can include chromaticdispersion optics along the optical path between the illumination unit318 and the imaged object, such that each wavelength of light is focusedto a different focal depth. Accordingly, the focused and unfocused areasof each monochromatic image may differ based on the particularillumination wavelength used. Suitable image processing algorithms canbe used to identify the focused areas of each image in order to increasethe clarity and precision of the final composite image.

An intraoral scanning procedure may involve capturing topographical scandata of multiple portions of the patient's intraoral cavity. Aspreviously described, the user can view the image data provided by theviewfinder (e.g., via a graphical interface provided on a display, asdescribed in further detail herein) in order to determine which portionsof the intraoral cavity are included in the current field of view of thescanner. Furthermore, suitable guidance mechanisms can be implemented toindicate to the user which portions of the cavity have already beenscanned in order to improve scanning efficiency and reduce unnecessaryrescanning. These guidance mechanisms can include visual indicatorsprovided on a display (e.g., as an overlay on top of the currentviewfinder image) that permit the user to rapidly and accurately assesswhether the current field of view is situated at an appropriate locationrelative to the areas of previous scan coverage. The user can thenposition and orient the field of view of the scanner accordingly so asto scan targeted portions of the intraoral cavity while reducing theoverlap with previously scanned areas. In many embodiments, the visualindicators can be updated or adjusted according to the scanning progressand scanner movement, thereby providing real-time or near real-timescanning guidance.

FIG. 5A illustrates a method 400 for guiding scanning of an intraoralcavity of a patient, in accordance with many embodiments. As with allmethods presented herein, any embodiment of the systems and devicesdescribed herein can be used to practice the method 400 and at leastsome of the steps of the method 400 can be performed by one or moreprocessors of a controller or other computing system.

In step 402, a viewfinder image corresponding to a current field of viewof an intraoral scanner is displayed (e.g., on the display 220). Asdescribed herein, the viewfinder image may comprise video image datacaptured by a suitable imaging device such as a camera. The displayedviewfinder images can be updated at a suitable rate (e.g., approximately30 Hz) so as to provide real-time or approximately real-time updates ofthe field of view as the scanner is moved relative to the intraoralcavity. In embodiments where the extent of the viewfinder image differsfrom the extent of the scanner field of view, one or more markers can bedisplayed on the viewfinder image in order to allow the user to identifythe portions of the viewfinder image that overlap with the scanner fieldof view. For example, graphical elements such as symbols, shapes,coloring, textures, etc. can be overlaid onto the viewfinder image inorder to delineate the spatial relationship of the field of view of thescanner relative to the displayed viewfinder image.

In step 404, one or more indicators of previously scanned portions ofthe intraoral cavity are displayed (e.g., on the display 220). Exemplarymethods for determining the extent of previously scanned portions andgenerating corresponding indicators are described in greater detailbelow. The one or more indicators can comprise suitable graphicalelements (e.g., symbols, shapes, text, coloring, textures, instructions,animations) positioned at one or more locations on the display so as toprovide visual guidance to a user (e.g., dental practitioner) indicatingwhich portions of the cavity have been already been scanned. Forexample, the indicators can comprise lines, borders, shading, coloring,etc. displayed at one or more locations so as to identify a boundary ofthe area of overlap. The indicators at the one or more locations can beused to mark one or more boundary locations of the area of overlap. Inmany embodiments, the one or more indicators are overlaid onto thedisplayed viewfinder image, thereby indicating the extent of thepreviously scanned portions relative to the current field of view of thescanner. Optionally, the one or more indicators may be overlaid ontoviewfinder images subsequent to the image of step 402, e.g., inembodiments where the viewfinder video rate differs from the indicatorupdate rate, as described in further detail below.

Furthermore, the indicators can also be used to warn the user ofpotential problems, such as insufficient overlap with previous scansthat would result in gaps in scanning coverage, or excessive overlapwith previous scans that would reduce scanning efficiency. For example,a warning indicator can be displayed if the amount of overlap is smallerthan a predetermined amount. In some instances, the warning indicatorcan be displayed if the amount of overlap is zero. The predeterminedamount can be based on user input and/or a property of the scanningsystem. For example, the predetermined amount can be based on theminimum amount of overlap between scans needed for the scanning systemto properly reconstruct the scanned topography. Alternatively or incombination, the warning indicator can be displayed if the amount ofoverlap is greater than a predetermined amount. For example, the warningindicator can be used to alert the user that sufficient scan data forthe corresponding portion of the intraoral cavity has already beenobtained. The warning indicator can be any suitable indicator includingor more of text, numbers, symbols, lines, shapes, coloring, shading, orblurring, as previously described. Optionally, the warning indicator cancomprise an audible warning, such as a sound, tone, or spoken alert.

In step 406, the intraoral scanner is positioned, the positioning beingguided at least in part by the one or more indicators. The viewfinderimage and/or indicators can be updated in real-time or approximatelyreal-time as the scanner is moved. For instance, as the user moves thescanner to adjust the portion of the intraoral cavity within the fieldof view of the scanner, the indicators can move correspondingly tocorrectly depict the previously scanned portions relative to theintraoral cavity portion. Accordingly, the user can reposition the fieldof view of the scanner within the intraoral cavity, for example, toadjust the amount of overlap between scans, verify the extent of scancoverage, and/or identify unscanned regions. For example, in response toa warning indicator alerting the user to insufficient overlap, the usercan maneuver the scanner to increase the area of overlap between thecurrent viewfinder image and the previously scanned portion of theintraoral cavity.

In step 408, a topography scan of a portion of the intraoral cavity isgenerated using the intraoral scanner, in accordance with theembodiments presented herein. The topography scan can be performed whilethe one or more indicators are being shown (e.g., at one or morelocations on the display).

In many embodiments, the method 400 can be repeated throughout theduration of a scanning procedure in order to provide the user withreal-time tracking of scanning progress. The displayed indicators can beupdated with each topography scan so as to reflect the current extent ofscanning coverage. Additionally, the locations of the displayedindicators on the display can be adjusted as the current viewfinderimage changes (e.g., based on changes to the position and/or orientationof the intraoral scanner) so that the user can ascertain the degree towhich the current field of view overlaps with previous scan data.

The scanning guidance mechanisms provided herein can utilize variousapproaches in order to determine and display the extent of previous scancoverage relative to a current viewfinder image. In many embodiments,areas of previous scan coverage within a current viewfinder image areidentified based on previously obtained viewfinder images. For example,the viewfinder can be configured to capture and store viewfinder imagescorresponding to the topography scans generated by the scanner. Eachrecorded viewfinder image can provide a representation of the portion ofthe intraoral cavity covered by the corresponding topography scan. Therecorded viewfinder images can be compared to a current viewfinder imagedepicting the current field of view of the scanner in order to identifyscanned and unscanned areas, e.g., by determining the area of overlapbetween the current viewfinder images and recorded viewfinder images.The area of overlap can be displayed to the user using the indicatorsdescribed herein.

FIG. 5B illustrates a method 420 for determining overlap between acurrent viewfinder image and previous scanning coverage, in accordancewith many embodiments. The steps of the method 420 can be practiced incombination with or in place of any of the steps of the other methodspresented herein, such as the method 400.

In step 422, an intraoral scanner is positioned so that a first portionof an intraoral cavity is within the field of view of the scanner.

In step 424, the first portion is scanned in order to generate atopography scan thereof. The topography scan can be performed using anysuitable method, such as the approaches previously described herein. Inembodiments where the intraoral scanner is a point-and-shoot scanner, auser input may be required in order to trigger the scan event.Alternatively, a continuous scanner may allow for multiple scan eventswithout requiring a user input to initiate each event, such that thescanning of the first portion is performed automatically orsemi-automatically. The resultant topography scan data can be stored asuitable location (e.g., in the memory 240 of the system 200).

In step 426, a first viewfinder image of the first portion correspondingto the topography scan is captured and stored (e.g., in the memory 240of the system 200). Optionally, the first viewfinder image can be acomposite color image produced from a plurality of monochromatic imagesgenerated using different illumination wavelengths, as described herein.The step 426 can be performed simultaneously with the step 424, suchthat the viewfinder image is recorded simultaneously with the topographyscan. Alternatively, the step 426 can be performed prior to or after thestep 424, such that the viewfinder image is recorded at a different timethan the topography scan. In many embodiments, the time interval betweenthe steps 424 and 426 is sufficiently short such that the scannerremains in approximately the same position and orientation for thetopography scanning and viewfinder imaging, thereby ensuring that thefirst viewfinder image provides an accurate representation of thecoverage of the topography scan.

In step 428, the intraoral scanner is positioned so that a secondportion of the intraoral cavity is within the field of view. The secondportion may overlap wholly or in part with the first portion.Alternatively, the two portions may be entirely separate with nooverlapping areas.

In step 430, a second viewfinder image of the second portion iscaptured, in accordance with the embodiments presented herein.

In step 432, an area of overlap between the first and second viewfinderimages is determined. Any suitable device can be used to determine theoverlap, such as the processing unit 230 of the system 200. Varioustechniques can be used to determine the area of overlap. For example,suitable algorithms can be used to register the first and secondviewfinder images to each other, such as image mosaicing algorithms orother techniques known to those of skill in the art. In manyembodiments, a feature-based method can be implemented in order toregister the images. For example, the image data can be analyzed toidentify one or more features present in both the viewfinder image andthe reference images. Suitable features can comprise points, corners,edges, boundaries between two colors, and the like. Accordingly, theimages can be registered based on identification and matching ofcorresponding features. Alternatively or in combination, the imageregistration can be performed using an intensity-based method. Forexample, an intensity-based method can comprise determining, based onthe pixel intensities of the images, transformations and/or deformationsof the viewfinder image that would place it in the greatest similarity(e.g., based on a suitable similarity measure) with the referenceimages. Accordingly, the images can be registered by transforming and/ordeforming the viewfinder image such that its similarity to the referenceimages is increased.

Following image registration, the area of overlap can be determined. Thearea of overlap can comprise a plurality of discontinuous areas, suchthat the overall area is computed as the sum of the discontinuous areas.Alternatively, the area of overlap can comprise a single continuousarea. The area of overlap can encompass the entire viewfinder image, forexample, if the second viewfinder image is completely overlapped by thefirst viewfinder image. The area of overlap can be zero, for example, ifthere is no overlap between the first and second viewfinder images. Thearea of overlap can be digitally represented by any suitable method. Forexample, a suitable algorithm can be used to compute a set of pixelcoordinates representing the boundary of the area of overlap withrespect to the second viewfinder image. Alternatively or in combination,the area can be represented as one or more of straight lines, curvedlines, or a polygon or other suitable shape.

In step 434, the one or more indicators of the area of overlap aredisplayed (e.g., on a screen or monitor of the display 220). Theindicators can be presented as a graphical overlay on the secondviewfinder image, such that the user can visually identify areas of thesecond viewfinder image that were covered in the topography scan, asdescribed herein.

In many embodiments, the steps 428, 430, 432, and 434 can be repeated,as indicated by the dashed line in FIG. 5B, thereby updating thedisplayed viewfinder image and indicators as the scanner is movedthrough a plurality of different positions relative to the intraoralcavity. At each position, the area of overlap between the currentviewfinder image and the first viewfinder image is calculated, therebyallowing the user to observe the extent to which the current viewfinderimage overlaps with the generated topography scan.

A scanning procedure may comprise positioning the scanner at variouslocations relative to the patient's intraoral cavity in order to collectmultiple topography scans. In many embodiments, a viewfinder image isrecorded for each corresponding topography scan, and the currentviewfinder image is compared to all of the stored viewfinder images inorder to determine the overlap between the current field of view and allprevious topography scans. This approach can allow the user to trackscanning progress for the entire procedure, thereby improvingflexibility and user convenience. In alternative embodiments, thecurrent viewfinder image may be compared to only a subset of the storedviewfinder images. For example, the current viewfinder image may becompared to a stored viewfinder image corresponding to the most recenttopography scan(s). This approach may be advantageous in terms ofreducing the amount of computation and processing time needed todetermine the area of overlap.

FIG. 5C illustrates a method 440 for tracking scanning progress, inaccordance with many embodiments. The steps of the method 440 can bepracticed in combination with or in place of any of the steps of theother methods presented herein, such as the method 400 or the method420.

In step 442, one or more stored viewfinder images are provided, eachcorresponding to a topography scan of an intraoral cavity generated byan intraoral scanner. The stored viewfinder images can be any suitableset of images corresponding to previously scanned portions of theintraoral cavity and can be stored in a suitable device (e.g., memory240). In many embodiments, the stored viewfinder images are imagesrecorded by the viewfinder in conjunction with previous topographyscans, as previously described herein. As discussed above, the storedviewfinder images may comprise a plurality of images taken during theentire scanning procedure, or may comprise only a single imagecorresponding to a single previous topography scan (e.g., theimmediately preceding scan). Optionally, the stored viewfinder imagescan comprise at least one composite image produced by registering andmerging a series of previously recorded viewfinder images with eachother (e.g., an image mosaic), such that the composite image correspondsto the scanning coverage over a plurality of previous scans.

In step 444, one or more indicators of an area of overlap between aviewfinder image and the one or more stored viewfinder images aredisplayed. The indicators can be displayed to the user as a graphicaloverlay on a viewfinder image corresponding to the current field of viewof the intraoral scanner. The indicators can be generated based on adetermined area of overlap between the stored viewfinder images and thecurrently displayed viewfinder image, using any of the techniquespreviously described herein. Alternatively, in embodiments where theindicators are generated and updated at a rate different from theviewfinder video rate, the indicators can be generated based on adetermined area of overlap between the stored viewfinder images and aviewfinder image different than the currently displayed viewfinder image(e.g., a viewfinder image captured one or more frames prior to thecurrently displayed viewfinder image). In many embodiments, theviewfinder image used for the overlap calculation is the same as orsimilar to currently displayed viewfinder image such that the displayedindicators provide an accurate representation of the previous scancoverage.

In step 446, the intraoral scanner is positioned guided by the one ormore indicators. In many embodiments, the indicators are updated as theintraoral scanner is moved so as to accurately reflect the extent ofscanning coverage relative to the current viewfinder image. As describedherein, the user can use the indicators to determine which portions ofthe intraoral cavity have already been scanned and aim the scannerdevice accordingly.

In step 448, a portion of the intraoral cavity is scanned to generate atopography scan thereof, as described herein.

In step 450, a viewfinder image corresponding to the topography scan iscaptured and stored, as described herein. The step 450 may occurconcurrently with, prior to, or after the step 448. The viewfinder imagecan be stored in the same location as the one or more stored viewfinderimages (e.g., memory 240).

In step 452, the one or more stored viewfinder images are updated toinclude the viewfinder image corresponding to the topography scan.Accordingly, if the method 440 is subsequently repeated, the area ofoverlap in step 444 can be determined using the updated set of storedviewfinder images. The method 440 can be used to update the displayedindicators as new topography scans are acquired, therefore providingtracking of scanning progress. In embodiments where only a singleprevious viewfinder image is stored, the update step involves replacingthe previously viewfinder image with the newly recorded viewfinder imageof step 450. In alternative embodiments where the stored viewfinderimages comprise a plurality of previous viewfinder images, the updatingstep involves adding the viewfinder image of step 450 to the set ofstored viewfinder images.

FIGS. 6A through 6C illustrate viewfinder images with overlaidindicators, in accordance with many embodiments. FIG. 6A illustrates aviewfinder image 500 of an intraoral cavity portion prior to acquisitionof any scan data of that portion. Since no scan data has been obtained,the viewfinder image 500 does not include any overlaid indicators. FIG.6B illustrates a viewfinder image 502 after a first topography scancovering part of the intraoral cavity portion has been performed. Theimage 502 includes overlaid graphical indicators, including a dashedline 504 marking a boundary of the area of overlap between the currentfield of view and the first topography scan coverage, as well as shading506 spanning the area of overlap. Alternatively or in combination, theindicators can comprise other graphical elements, such as one or more ofan alphanumerical value, symbol, line, shape, or the like, as well ascoloring, shading, blurring, texturing, or other feature(s) of the areaof overlap suitable to distinguish it from the non-overlapping portionsof the viewfinder image. FIG. 6C illustrates a viewfinder image 508after a second topography scan covering additional parts of theintraoral cavity portion has been performed. The dashed line 510 andshading 512 correspond to the coverage of the first and secondtopography scans combined. The dashed line 510 and shading 512 cover alarger area of the viewfinder image 508 compared to FIG. 6B, indicatingthat the area of previous scan coverage has increased.

FIG. 7 illustrates a user interface 600 suitable for use with anintraoral scanning system, in accordance with many embodiments. The userinterface 600 can be presented to a user on a suitable display (e.g.,display 220). In many embodiments, the user interface 600 comprises aviewfinder window 602 used to display viewfinder image datacorresponding to the field of view of the intraoral scanner. Theviewfinder window 602 can provide a real-time or approximately real-timevideo stream of the viewfinder image data. As described herein, visualindicators (not shown) can be overlaid onto the viewfinder imagesdisplayed in the viewfinder window 602 so as to allow the user toidentify previously scanned portions of the intraoral cavity.Optionally, the user interface 600 can also comprise a separate scanningwindow 604 used to present surface topography data obtained during thescanning procedure, e.g., as a three-dimensional virtual model. Inalternative embodiments, the scanning window 604 can be presented on aseparate display from the viewfinder window 602. Suitable controlcommands can be used to manipulate the virtual model in the scanningwindow 604 (e.g., zoom in, zoom out, rotate, translate), such as controlcommands generated based on user input (e.g., via the input unit 210).In many embodiments, the virtual model can be updated in real time sothat the user can immediately see the results of the latest scan. Thus,during the scanning procedure, the user can ensure satisfactory scanoverlap and coverage, guided at least in part by current viewfinderimage and one or more indicators of the viewfinder window 602, and alsoverify scanning progress, based at least in part on the reconstructedsurface topography of the virtual model of the scanning window 604.

The various techniques described herein may be partially or fullyimplemented using code that is storable upon storage media and computerreadable media, and executable by one or more processors of a computersystem. The processor can comprise array logic such as programmablearray logic (hereinafter PAL), configured to perform the techniquesdescribed herein. Storage media and computer readable media forcontaining code, or portions of code, can include any appropriate mediaknown or used in the art, including storage media and communicationmedia, such as but not limited to volatile and non-volatile, removableand non-removable media implemented in any method or technology forstorage and/or transmission of information such as computer readableinstructions, data structures, program modules, or other data, includingRAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM,digital versatile disk (DVD) or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to store thedesired information and which can be accessed by the a system device.Based on the disclosure and teachings provided herein, a person ofordinary skill in the art will appreciate other ways and/or methods toimplement the various embodiments.

While preferred embodiments of the present invention have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the invention. It should be understoodthat various alternatives to the embodiments of the invention describedherein may be employed in practicing the invention. It is intended thatthe following claims define the scope of the invention and that methodsand structures within the scope of these claims and their equivalents becovered thereby.

What is claimed is:
 1. A system comprising: a memory; and a processingdevice operatively connected to the memory, the processing device to:make a comparison between a current image of an oral cavity of a patientand one or more previously received images of the oral cavity of thepatient, the current image and the one or more previously receivedimages having been generated by an intraoral scanner; determine anamount of overlap between a current field of view of the intraoralscanner and topography scans of the oral cavity based on the comparison;and output a warning indicator associated with a positioning of thecurrent field of view of the intraoral scanner responsive to determiningthat the amount of overlap fails to meet or exceed an overlap threshold.2. The system of claim 1, wherein the warning indicator is a coloredborder output to a display.
 3. The system of claim 1, wherein thewarning indicator comprises an audio warning.
 4. The system of claim 1,wherein the one or more previously received images comprise thetopography scans, and wherein the current image is associated with thecurrent field of view of the intraoral scanner.
 5. The system of claim1, wherein the one or more previously received images and the currentimage comprise color viewfinder images.
 6. The system of claim 1,wherein the processing device is further to: generate athree-dimensional model of one or more surfaces within the oral cavityusing topographical information associated with the topography scans;and output the three-dimensional model to a display.
 7. The system ofclaim 6, wherein at least one of a position or orientation of thethree-dimensional model relative to the warning indicator on a displaychanges as the intraoral scanner is repositioned in the oral cavity. 8.The system of claim 6, wherein the processing device is further to:capture a new image of the oral cavity; make a new comparison betweenthe new image and the one or more previously received images; determinea new amount of overlap between the current field of view of theintraoral scanner and the topography scans of the oral cavity based onthe new comparison; determine whether or not the new amount of overlapmeets or exceeds the overlap threshold; and update the warning indicatorbased on whether or not the new amount of overlap meets or exceeds theoverlap threshold.
 9. The system of claim 1, wherein the warningindicator provides real-time visual guidance of scanning coverage duringscanning of the oral cavity.
 10. The system of claim 1, wherein theprocessing device is further to: perform a registration operationbetween the current image and the one or more previously received imagesbased on identifying one or more features present in both the currentimage and the one or more previously received images; and determine theamount of overlap based on the registration operation.
 11. The system ofclaim 1, wherein the overlap threshold is based on a minimum amount ofoverlap needed to reconstruct a surface topology of the oral cavity. 12.The system of claim 1, wherein the processing device is further to:display image data from at least one of a) the current image or b) theone or more previously received images.
 13. The system of claim 1,wherein the processing device is further to: receive the current imageof the oral cavity, the current image having been generated by theintraoral scanner by measuring one or more characteristics of returninglight, the returning light having been reflected off one or moresurfaces within the oral cavity.
 14. A non-transitory computer readablemedium comprising instructions that, when executed by a processing unit,cause the processing unit to perform operations for guiding scanning ofan oral cavity of a patient, the operations comprising: making acomparison between a current image of an oral cavity of a patient andone or more previously received images of the oral cavity of thepatient, the current image and the one or more previously receivedimages having been generated by an intraoral scanner; determining anamount of overlap between a current field of view of the intraoralscanner and topography scans of the oral cavity based on the comparison;and output a warning indicator associated with a positioning of thecurrent field of view of the intraoral scanner responsive to determiningthat the amount of overlap fails to satisfy an overlap threshold. 15.The non-transitory computer readable medium of claim 14, wherein thewarning indicator is a colored border output to a display.
 16. Thenon-transitory computer readable medium of claim 14, wherein the warningindicator comprises an audio warning.
 17. The non-transitory computerreadable medium of claim 14, the operations further comprising:displaying image data from at least one of a) the current image or b)the one or more previously received images.
 18. The non-transitorycomputer readable medium of claim 14, the operations further comprising:receiving the current image of the oral cavity, the current image havingbeen generated by the intraoral scanner by measuring one or morecharacteristics of returning light, the returning light having beenreflected off one or more surfaces within the oral cavity.
 19. Thenon-transitory computer readable medium of claim 14, wherein the one ormore previously received images comprise the topography scans, andwherein the current image is associated with the current field of viewof the intraoral scanner.
 20. The non-transitory computer readablemedium of claim 14, wherein the one or more previously received imagesand the current image comprise color viewfinder images.
 21. Thenon-transitory computer readable medium of claim 14, the operationsfurther comprising: generating a three-dimensional model of one or moresurfaces within the oral cavity using topographical informationassociated with the topography scans; and outputting thethree-dimensional model to a display.
 22. The non-transitory computerreadable medium of claim 21, wherein at least one of a position or anorientation of the three-dimensional model relative to the warningindicator on a display changes as the intraoral scanner is repositionedin the oral cavity.
 23. The non-transitory computer readable medium ofclaim 14, the operations further comprising: capturing a new image ofthe oral cavity; making a new comparison between the new image and theone or more previously received images; determining a new amount ofoverlap between the current field of view of the intraoral scanner andthe topography scans based on the new comparison; determining whether ornot the new amount of overlap meets or exceeds the overlap threshold;and updating the warning indicator based on whether or not the newamount of overlap meets or exceeds the overlap threshold.
 24. Thenon-transitory computer readable medium of claim 14, wherein the warningindicator provides real-time visual guidance of scanning coverage duringscanning of the oral cavity.
 25. The non-transitory computer readablemedium of claim 14, the operations further comprising: performing aregistration operation between the current image and the one or morepreviously received images based on identifying one or more featurespresent in both the current image and the one or more previouslyreceived images; and determining the amount of overlap based on theregistration operation.
 26. The non-transitory computer readable mediumof claim 14, wherein the overlap threshold is based on a minimum amountof overlap needed to reconstruct a surface topology of the oral cavity.